Artificial heart with energy recovery

ABSTRACT

An apparatus for use in an artificial heart assembly includes an internal coil adapted to be implanted beneath the skin of a subject and an external coil coupled to transmit electric power to the internal coil through the skin of the subject. The apparatus includes a DC-to-AC converter coupled to the external coil which selectively converts DC power from a DC power source into either a first frequency or a second frequency, the first frequency having a plurality of cycles each of a first duration and the second frequency having a plurality of cycles each of a second duration longer than the first duration. The DC-to-AC converter comprises four switching components each coupled in parallel with a respective one of four passive components and a drive circuit operatively coupled to the switching components. The drive circuit causes the switching components to be switched to a nonconductive state so that they are nonconductive for a time period and so that electric current flows through a plurality of the passive components during that time period.

This patent is subject to Government Contract No. N01-HV-38130 with theNational Institutes of Health.

BACKGROUND OF THE INVENTION

The present invention is directed to an artificial heart apparatus withan energy recovery circuit.

U.S. Pat. No. 5,674,281 to Snyder discloses an artificial heart assemblyhaving a blood inlet conduit, a blood outlet conduit, and a pumpingmechanism that pumps blood from the blood inlet conduit to the bloodoutlet conduit. The Snyder artificial heart assembly includes a firstmembrane defining a blood chamber fluidly coupled to the blood inletconduit and the blood outlet conduit, and the pumping mechanism includesa pusher plate that makes contact with the first membrane to force bloodfrom the blood inlet conduit to the blood outlet conduit. The Snyderartificial heart assembly also has a second membrane defining a secondblood chamber fluidly coupled to a second blood inlet conduit and asecond blood outlet conduit and a second pusher plate that makes contactwith the second membrane to force blood from the second blood inletconduit to the second blood outlet conduit.

U.S. Pat. No. 5,728,154 to Crossett, et al. discloses an artificialheart assembly that has a structure similar to the artificial heartassembly described above in connection with the Snyder patent. TheCrossett, et al. patent also discloses a communications system thatincludes an external transceiver located external of a subject and aninternal transceiver that is implanted beneath the skin of a subject.The internal transceiver is provided with an internal coil.

U.S. Pat. No. 5,751,125 to Weiss discloses an artificial heart assembly,which is provided either as a total artificial heart or as a ventricularassist device, having a sensorless motor and a circuit for reversiblydriving the sensorless motor.

U.S. Pat. No. 5,630,836 to Prem, et al. discloses a transcutaneousenergy and data transmission apparatus for a cardiac assist device suchas an artificial heart or ventricular assist device. The transmissionapparatus has an external coupler in the form of a tuned circuit with aninduction coil and an internal coupler which together act as an air-coretransformer. The transmission apparatus has a DC power supply and apower converter that are coupled to the external coupler. The powerconverter converts electric current from the DC power supply intohigh-frequency AC. The transmission apparatus has a voltage regulatorcoupled to the internal coupler. As shown in FIG. 3 and described inconnection therewith, the Prem, et al. patent discloses that the voltageregulator includes a shunt switch and a shunt controller. As shown inFIG. 2, the power converter includes an H-bridge inverter, an H-bridgecontroller, and a shunt detector. The H-bridge controller can reduce theduty cycle of the H-bridge converter if a shunt is detected.

SUMMARY OF THE INVENTION

The invention is directed to an apparatus for use in an artificial heartassembly having a blood inlet conduit, a blood outlet conduit, and apump that is adapted to pump blood from the blood inlet conduit to theblood outlet conduit. The apparatus includes an internal coil adapted tobe implanted beneath the skin of a subject and an external coil adaptedto be disposed adjacent the internal coil and separated from theinternal coil by the skin of the subject, the external coil beingcoupled to transmit electric power to the internal coil through the skinof the subject.

The apparatus includes a DC-to-AC converter coupled to the external coiland to a source of DC power. The DC-to-AC converter selectively convertsDC power from the DC power source into either a first frequency or asecond frequency, the first frequency having a plurality of cycles eachof a first duration and the second frequency having a plurality ofcycles each of a second duration longer than the first duration.

The DC-to-AC converter comprises a first switching component coupled inparallel with a first passive component, a second switching componentcoupled in parallel with a second passive component, a third switchingcomponent coupled in parallel with a third passive component, a fourthswitching component coupled in parallel with a fourth passive component,and a drive circuit operatively coupled to the switching components. Thedrive circuit causes all four of the switching components to be switchedto a nonconductive state so that the four switching components arenonconductive for a time period and so that electric current flowsthrough a plurality of the passive components during that time period.

The drive circuit may cause all four of the switching components to beswitched to a nonconductive state for a time period at least as long asthe first duration, or for a time period at least twice as long as thefirst duration.

The first switching component may be connected to the second switchingcomponent at a first junction, the second switching component may beconnected to the third switching component at a second junction, thethird switching component may be connected to the fourth switchingcomponent at a third junction, and the fourth switching component may beconnected to the first switching component at a fourth junction. Thefourth junction may be connected to the DC power source, the secondjunction may be connected to a ground potential, and the external coilmay be connected between the first and third junctions. The switchingcomponents may comprise transistors, and the passive components maycomprise diodes.

The features and advantages of the present invention will be apparent tothose of ordinary skill in the art in view of the detailed descriptionof the preferred embodiment, which is made with reference to thedrawings, a brief description of which is provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the mechanical portions of an artificialheart assembly, portions of which are shown in cross section;

FIG. 2 is a cross-sectional side view of a pair of coils used inconnection with an embodiment of the invention;

FIG. 3 is an overall block diagram of an embodiment of the electricalportions of an artificial heart assembly;

FIG. 4 is a circuit diagram of a DC-to-AC converter shown schematicallyin FIG. 3;

FIG. 5 is a block diagram of one embodiment of a controller shownschematically in FIG. 3;

FIG. 6 is a circuit diagram of a first embodiment of the power circuitshown schematically in FIG. 3;

FIGS. 7A-7C illustrate various voltage waveforms generated duringoperation of the power circuit;

FIG. 8 illustrates the change in the voltage on a power supply capacitorinduced by a voltage modulating circuit;

FIGS. 9A-9B illustrate a number of data waveforms;

FIG. 10 is a circuit diagram of an alternative power circuit;

FIG. 11 is a circuit diagram of another embodiment of a power circuit;

FIG. 12 is an alternative embodiment of an external assembly;

FIGS. 13A-13G illustrate various waveforms in connection with a datatransmission method;

FIGS. 14 and 15 are flowcharts of software routines that may be used inconnection with the data transmission method;

FIGS. 16A and 16B illustrate a set of waveforms for driving a DC-to-ACconverter at one frequency during a power-supply mode and at a secondfrequency during an idle mode;

FIGS. 17A and 17B illustrate a set of waveforms for driving a DC-to-ACconverter at two different frequencies and with an energy recovery mode;

FIGS. 18A and 18B illustrate current flows through the AC-to-DCconverter shown in FIG. 16;

FIG. 19 illustrates an alternative embodiment of the AC-to-DC convertershown schematically in FIG. 4 and an alternative embodiment of acontroller shown schematically in FIG. 5;

FIG. 20 is a block diagram of a controller;

FIG. 21 is a graph illustrating a range of phase shifts between voltageand current;

FIG. 22 illustrates an embodiment of a metal detection and power supplycircuit;

FIG. 23 is a circuit diagram of one embodiment of a phase detector shownschematically in FIG. 22;

FIGS. 24A-24F are waveforms illustrating the operation of the phasedetector of FIG. 23; and

FIG. 25 is a flowchart illustrating one example of the operation of thecontroller shown in FIG. 22.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

FIG. 1 illustrates the mechanical portions of an artificial heartassembly 10 which may be implanted within a subject, such as a human oran animal, to take the place of the subject's natural heart. As definedherein, an artificial heart assembly intended for use with a subject,such as an animal or human, may be a total artificial heart (TAH)intended to replace the entire heart of the subject, a ventricularassist device (VAD) intended to replace a portion of the subject'sheart, or an external blood pump to be used with the subject.

The artificial heart assembly 10 has a housing 12 composed of threesections 12 a, 12 b, 12 c which are held together by a pair of annularV-rings 14, 16. A blood reservoir within a sac 18 disposed within thehousing section 12a is fluidly coupled to a blood outlet defined by anartificial vascular graft 20 connected to the housing section 12 a via athreaded connector 22. The graft 20 may be connected to the pulmonaryartery of the subject via a suture line 24. The blood reservoir withinthe sac 18 may be fluidly coupled to a blood inlet chamber defined by anartificial graft 26 which may be connected to the housing section 12 avia a threaded connector 28 and to the right atrium of the subject via asuture line (not shown). A pair of one-way check valves (not shown) maybe disposed in the blood inlet 26 and the blood outlet 20 to ensure thatblood is pumped in the direction shown by the arrows in FIG. 1.

A blood sac 38 disposed within the housing section 12 c may be fluidlycoupled to a blood outlet defined by an artificial graft 40 connected tothe housing section 12 c via a threaded connector 42. The graft 40 maybe connected to the aorta of the subject via a suture line 44. The bloodreservoir in the blood sac 38 may be coupled to a blood inlet chamberdefined by an artificial graft 46 which is connected to the housingsection 12 c via a threaded connector 48 and to the left atrium of thesubject via a suture line (not shown). A pair of one-way check valves(not shown) may be disposed in the blood inlet 46 and the blood outlet40 to ensure that blood is pumped in the direction shown by the arrows.

A pumping mechanism or pump 29 may be provided to pump blood from theblood inlet 26 to the blood outlet 20 and from the blood inlet 46 to theblood outlet 40. The pumping mechanism 29 has a pumping structure and amotor operatively coupled to drive the pumping structure. The pumpingstructure may be provided, for example, in the form of a pusher plate 30that makes contact with and periodically deforms the blood sac 18 toforce blood from the blood inlet 26 to the blood outlet 20 and a pusherplate 50 that makes contact with and periodically deforms the blood sac38 to force blood from the blood inlet 46 to the blood outlet 40.

The pump 29 may include a DC brushless motor 52 that drives the pusherplates 30, 50 laterally back and forth. The motor 52 may be coupled tothe pusher plates 30, 50 via a drive screw 54 and a coupling mechanismcomposed of a plurality of threaded elongate rollers 56 disposed withina cylindrical nut 58 fixed to a rotor (not shown) of the motor 52.Rotation of the rotor causes the nut 58 and rollers 56 to rotate, thuscausing the drive screw 54 to be linearly displaced in a directionparallel to its longitudinal central axis. A guide rod 62 may beconnected between the two pusher plates 30, 50 to pass through a fixedbushing 64 to prevent the plates 30, 50 from rotating. Other mechanismsfor coupling the rotor to the pusher plates 30, 50 could be used.

The rotation of the rotor may be controlled via the electricalenergization of a plurality of windings of a stator (not shown) which isrotatably coupled to the rotor via a pair of cylindrical bearings 72. Awire port 74 may be formed in the housing section 12 b to allow thepassage of wires from the windings to a controller 76 (FIG. 3), whichmay be implanted in another area of the subject, such as in thesubject's abdomen.

The structural details of the artificial heart assembly 10 and thepumping mechanism 29 described above are exemplary only and are notconsidered important to the invention. Alternative designs could beutilized without departing from the invention.

Overall Assembly

FIG. 3 is an overall block diagram of the electrical portions of theartificial heart assembly 10. Referring to FIG. 3, the artificial heartassembly 10 has an external assembly 90 that is provided at an externallocation outside of a subject and an internal assembly 100 that isimplanted within the subject.

The external assembly 90 includes a DC power source 102 and a DC-to-ACconverter 104 connected to the DC power source via a conductive line106. The DC power source 102, which may be a portable battery or batterypack providing a DC voltage of between 10 and 18 volts, for example,supplies a DC voltage to the DC-to-AC converter 104, which converts thatDC voltage into a high-frequency voltage. That high-frequency voltage isprovided to an external coil network 108 via a pair of conductors 110,112. A current sensor schematically shown and designated 114 may be usedto sense the magnitude of the electric current flowing within theconductor 112, and a controller 116 connected to the current sensor 114via a conductor 118 may be used to control the operation of the DC-to-ACconverter 104, via a control line 120, based on one or morecharacteristics of the current sensed by the sensor 114.

The external coil network 108, which is disposed adjacent the skin ofthe subject, transfers electric power through the skin of the subject toan internal coil network 130 disposed beneath the skin of the subject.The internal coil network 130 is connected to a power circuit 132 via apair of conductors 134, 136, and the power circuit 132 supplies electricpower to the controller 76 via a pair of conductors 142, 144. Thecontroller 76 may control the operation of the motor 52 through a motordrive circuit 146. The power conductors 142, 144 also supply electricpower to the motor 52 through the drive circuit 146.

The internal assembly 100 could also include an auxiliary power supplycircuit 147 having a rechargeable battery, such as the circuit disclosedin U.S. Ser. No. 09/557,819 filed herewith and entitled “ArtificialHeart With Arrhythmia Signalling” for which Alan Snyder is the namedinventor.

The motor drive circuit 146 could be composed of a commutator (notshown) and a driver circuit (not shown), as disclosed in U.S. Pat. No.5,751,125 to Weiss, which is incorporated herein by reference. Thecontroller 76 could be used to operate the motor 52 in the mannerdisclosed in U.S. Pat. No. 5,751,125 to Weiss and/or U.S. Pat. No.5,674,281 to Snyder, both of which patents are incorporated herein byreference. However, the particular manner in which the motor 52 iscontrolled is not considered important to the invention.

External and Internal Coils

The external coil network 108 may include an external coupler in theform of an electromagnetic transformer coil 150 (FIG. 4) and a capacitor148 (FIG. 4) connected in series with the external coil 150. Theinternal coil network 130 may include an internal coupler in the form ofan electromagnetic transformer coil 152 (FIG. 6) and a capacitor 154connected in series.

Referring to FIG. 2, the internal coil 152 is disposed beneath the skin156 of a subject, and the external coil 150 is disposed generallyadjacent the internal coil 152. The internal coil 152 may have aplurality of conductive windings 158 disposed in a circular insulatingmember 160, and the external coil 150 may have a plurality of conductivewindings 162 disposed in an insulating ring 164. As is known, theinductance of each of the coils 150, 152 is determined by the number,diameter and spacing of the windings 158, 162. The inductive orelectromagnetic coupling between the coils 150, 152 is a function oftheir physical proximity, their operating frequency, and theirinductances. Coils of other shapes and structures could be used.

The coils 150, 152 together constitute a loosely coupled transformer,with the external coil 150 acting as a primary winding and the internalcoil 152 acting as a secondary winding. The coils 150, 152 and thecapacitors 148, 154 with which they may be connected may form a resonantcircuit. The coils 150, 152 may be tuned to the same, or different,resonant frequencies. For example, the coils 150, 152 may be seriestuned to a power transmission frequency of about 200 kHz.

The external coil 150 may induce an electric current in the internalcoil 152, and the internal coil 152 may induce an electric current inthe external coil 152, in accordance with the following equations:

I _(EXT) =V _(INT)(2 πfk{square root over (L_(EXT)L_(INT)))}  [1]

I _(INT) =V _(EXT)(2 πfk{square root over (L_(EXT)L_(INT)))}  [2]

where I_(EXT) is the current induced in the external coil network 108,where I_(INT) is the current induced in the internal coil network 130,where V_(EXT) is the voltage across the external coil network 108, whereV_(INT) is the voltage across the internal coil network 130, where f isthe frequency of the voltage across the coils 150, 152, where L_(EXT) isthe inductance of the external coil 150, where L_(INT) is the inductanceof the internal coil 152, where k is a constant, and where the coilnetworks are tuned to the same frequency f.

DC-to-AC Converter 104

FIG. 4 is a circuit diagram of the DC-to-AC converter 104 shownschematically in FIG. 3 and also shows the external coil network 108.Referring to FIG. 4, the DC-to-AC converter 104 may comprise fourtransistors 170, 172, 174, 176, which may be metal oxide field-effecttransistors (MOSFETs), connected in an H-bridge configuration. Each ofthe transistors 170, 172, 174, 176 is controlled by a respectivehigh-frequency drive signal provided on the conductor 120, with two ofthe drive signals being 180° out of phase, or complemented, with respectto the other two via an inverter 182. The drive signals may be 50% dutycycle square waves provided at a frequency of about 200 kHz, forexample. Although a particular type of DC-to-AC converter has beendescribed above, any type of electronic switching network that generatesa high-frequency voltage may be used.

Power Circuit 132 a

FIG. 6 illustrates the internal coil network 30 shown schematically inFIG. 3 and a power circuit 132 a, which is one possible embodiment ofthe power circuit 132 schematically shown in FIG. 3. Referring to FIG.6, the power supply circuit 132 a acts as a voltage regulator toregulate the voltage stored by a relatively large, power supplycapacitor 186. The voltage across the capacitor 186 is output via thelines 142, 144 to the controller 76 (FIG. 3) and to the pump 29 whichincludes the pump motor 52.

The power circuit 132 a includes an AC-to-DC converter 190 that performsfull wave rectification of the sinusoidal AC current induced in theinternal coil 152 by the external coil 150. The AC-to-DC converter 190may include four switching elements, which may be provided in the formof diodes or Schottky diodes 192, 194, 196, 198. The conductor 142 isconnected to the intersection 200 of the diodes 192, 194 and carries arelatively high output voltage, and the conductor 144 is connected tothe intersection 202 of the diodes 196, 198 and is grounded.

A switching transistor 204 is connected in parallel with the diode 196,and a switching transistor 206 is connected in parallel with the diode198. The switching transistors 204, 206 may be field-effect transistors,and they may have a pair of diodes 208, 210 integrally formed therewith.

A switching control circuit 220 may be provided to control theconductive state of the transistors 204, 206. The switching controlcircuit 220 may be provided with a comparator 222, a plurality ofbiasing resistors 224, 226, 228, a feedback resistor 230, and athreshold setting circuit, which may be in the form of a resistor 232and a Zener diode 234.

Operation of Power Circuit 132 a

During operation, the motor 52 drives the pusher plates 30, 50 in areciprocal fashion to pump blood through the artificial heart assembly10 as described above, drawing electric current from the power supplycapacitor 186. As current is drawn from the capacitor 186, the voltageacross the capacitor 186 will decrease.

To replenish the voltage on the capacitor 186, the power circuit 132 amay periodically operate in a power supply mode in which electriccurrent generated by the AC-to-DC converter 190 is provided to thecapacitor 186 via the line 142. When not operating in the power supplymode, the power circuit 132 operates in an idle mode in which current isnot supplied to the capacitor 186.

Whether the power circuit 132 a operates in the power supply mode or inthe idle mode may be controlled based on the magnitude of the outputvoltage across the power supply capacitor 186. For example, if theoutput voltage falls below a certain value, the power circuit 132 a mayoperate in the power supply mode. When the output voltage rises to acertain value, the power supply circuit 132 a may operate in the idlemode.

By selectively supplying current to the power supply capacitor 186 onlyduring certain times (i.e. the power supply mode), the voltage acrossthe capacitor 186 is regulated, or maintained within a predeterminedvoltage range, such as between about 13 and about 14 volts, for example.

FIG. 7A illustrates the magnitude of the voltage across the power supplycapacitor 186, which is referred to as V_(OUT), as it changes over time.Referring to FIG. 7A, V_(OUT) gradually decreases (during the idle mode)as current is drawn from the capacitor 186, and gradually increases(during the power supply mode) when current is supplied to the capacitor186 from the AC-to-DC converter 190.

Referring also to FIG. 6, whether the power circuit 132a is in the powersupply mode or the idle mode is controlled by the comparator 222, whichbasically compares a sensing voltage V_(SENSE) derived from V_(OUT) witha predetermined threshold voltage V_(REF). When V_(SENSE) is greaterthan V_(REF), the output voltage V_(CONTROL) of the comparator 222 ishigh and the power circuit 132 a is in the idle mode. When V_(SENSE) isnot greater than V_(REF), the output voltage V_(CONTROL) of thecomparator 222 is low and the power circuit is in the power supply mode.

Referring to FIG. 6, the inverting input of the comparator 222 isconnected to sense the voltage V_(REF) at the intersection of theresistor 232 and the Zener diode 234, which is a fixed voltage due tothe Zener diode 234. The noninverting input of the comparator 222 isconnected to sense the voltage V_(SENSE) at the intersection of theresistors 226, 228, which form a voltage divider of the output voltageon the power supply capacitor 186 since the resistors 226, 228 are inparallel with the capacitor 186.

The feedback resistor 230 may be used to provide hysteresis to ensurethat the power supply mode lasts for a minimum duration. Referring toFIG. 7B, when the value of V_(SENSE) drops below V_(REF) causingV_(CONTROL) to be a low voltage, the feedback resistor 230 causes thevalue of V_(SENSE) to drop further as shown in FIG. 7B (the value ofV_(SENSE) drops because the resistor 230 is essentially in parallel withthe resistor 228 when V_(CONTROL) is a low voltage). And when the valueof V_(SENSE) increases to reach V_(REF), causing V_(CONTROL) to be ahigh voltage, the feedback resistor 230 causes the value of V_(SENSE) toincrease further as shown in FIG. 7B (the value of V_(SENSE) increasesbecause the resistor 230 is no longer essentially in parallel with theresistor 228).

The conductive state of the transistors 204, 206 (which may be N-channelMOSFETs) is controlled by V_(CONTROL). When V_(CONTROL) is a lowvoltage, meaning that the power circuit 132 a is in the power supplymode, the transistors 204, 206 will both be turned off and will have arelatively high impedance and act essentially as open circuits. In thatcase, during one half-cycle, electric current will flow from electricalground at the conductor 144, down through the diode 198, up through theinternal coil 152, and down through the diode 192 to the conductor 142where it is supplied to charge the power supply capacitor 186. Duringthe next half-cycle, electric current will flow from electrical groundat the conductor 144, up through the diode 196, down through theinternal coil 152, and up through the diode 194 to the conductor 142where it is supplied to charge the power supply capacitor 186.

When V_(CONTROL) is a high voltage, meaning that the power circuit 132 ais in the idle mode, the transistors 204, 206 will both be turned on,have a relatively low impedance, and act essentially as short circuitsto short out the diodes 196, 198 with which they are in parallel. Inthat case, electric current flowing upwards through the internal coil152 during one half-cycle will bypass the diode 192 that leads to theconductor 142 and will flow through the transistor 204 to ground.Electric current flowing downwards through the internal coil 152 duringthe next half-cycle will bypass the diode 194 that leads to theconductor 142 and will flow through the transistor 206 to ground.Consequently, little or no electric current is supplied to charge thecapacitor 186 during the idle mode.

Controller 116 a

FIG. 5 is a block diagram of a controller 116 a, which is one embodimentof the controller 116 shown schematically in FIG. 3. The controller 116achanges the frequency at which the DC-to-AC converter 104 operates toconserve electric power during the idle mode described above. During theidle mode, when electric current is not being supplied to the capacitor186, the power transmitted to the internal coil 152 by the external coil150 is reduced in order to conserve the power of the DC power source 102(FIG. 3), which may be a battery. This is accomplished by changing thefrequency at which the DC-to-AC converter 104 operates.

As noted above, the internal and external coils 150, 152 may be tuned toa power transmission frequency, such as 200 kHz. Consequently, when itis desired to transmit power to the internal coil 152, the DC-to-ACconverter 104 is operated at the power transmission frequency to whichit is tuned. However, when it is not necessary to transmit a significantamount of power, such as during the idle mode above, the frequency ofthe DC-to-AC converter 104 is changed.

For example, the frequency at which the DC-to-AC converter 104 operatesduring the power-supply mode may be changed to an odd subharmonic ofthat frequency during the idle mode. For example, the idle modefrequency may be ⅓, ⅕, {fraction (1/7)}, {fraction (1/9)} of the powersupply mode frequency. The amount of power transmitted to the internalcoil 152 varies with the idle mode frequency, with less power beingtransmitted at the seventh subharmonic (i.e. {fraction (1/7)} of thepower supply mode frequency, or 28.6 kHz if the power transmissionfrequency is 200 kHz) and more power being transmitted at the thirdsubharmonic (i.e. ⅓ of the power supply mode frequency). Since oddsubharmonics of a fundamental frequency still contain, in accordancewith Fourier analysis, some components of the fundamental frequency,using an odd subharmonic of the power supply mode frequency during idlemode will still result in some power being transmitted to the internalcoupler 152, which is generally desirable.

Referring to FIG. 5, the controller 116 a has a rectifier/filter circuit240 connected to the current sensor 114 (FIG. 3) via the line 118. Therectifier/filter circuit 240 generates a voltage that is provided to thenoninverting input of a comparator 242, which has its inverting inputconnected to receive a fixed threshold voltage V_(THRESH). Therectifier/filter circuit 240 and the comparator 242 act as anidle-mode-detection circuit to detect when the power circuit 132 a isoperating in the idle mode.

In particular, the rectifier/filter circuit 240 generates a voltage thatis indicative of the magnitude of the electric current flowing throughthe external coil 150, which current is proportional to the voltageacross the internal coil 152. During the idle mode, the transistors 204,206 are turned on and present relatively small impedances. Since thetransistors 204, 206 are connected essentially in parallel with theinternal coil network 130, when they are turned on during the idle mode,the transistors 204, 206 cause the voltage across the internal coilnetwork 130 to significantly decrease. That voltage decrease causes thecurrent induced in the external coil 150 to be significantly decreased,in accordance with Equation [1] set forth above. Consequently, thevoltage generated by the rectifier/filter circuit 240 decreasessignificantly when the power circuit 132 a is in the idle mode. Thecomparator 242 detects that decrease when the voltage provided to itsnoninverting input falls below the threshold voltage V_(THRESH) providedto its inverting input.

The output of the comparator 242 is connected to the select input of afrequency selector switch 244. The selector switch 244 has a firstfrequency input coupled to receive a drive signal having a firstfrequency, such as 200 kHz, generated by a frequency generator 246. Theselector switch 246 has a second frequency input connected to receive adrive signal output from a frequency divider 248, that may generate afrequency that is an odd subharmonic of the frequency generated by thefrequency generator 246.

When the power circuit 132 a is in the power-supply mode as detected bythe comparator 242, the selector switch 244 causes the drive signalgenerated by the frequency generator 246 to be supplied to the DC-to-ACconverter 104 via the line 120. When the power circuit 132 a is in theidle mode as detected by the comparator 242, the selector switch 244causes the drive signal generated by the frequency divider 248 to besupplied to the DC-to-AC converter 104 via the line 120.

Power Circuit 132 b

FIG. 10 illustrates the internal coil network 130 shown schematically inFIG. 3 and a power circuit 132 b, which is one possible embodiment ofthe power circuit 132 schematically shown in FIG. 3. Referring to FIG.10, the power circuit 132 b is similar to the power circuit 132 a shownin FIG. 6 and described above, except that a synchronous drive circuit250 is included between the transistors 204, 206 and the comparator 222.

The synchronous drive circuit 250 may be provided in the form of a pairof driver circuits 254, 256, such as MOSFET drivers, a pair of diodes264, 266 connected to the inputs of the driver circuits 254, 256, andfour resistors 268, 270, 272, 274. As shown in FIG. 10, the intersectionof the resistors 268, 270 is connected to the input of the drivercircuit 256, and the intersection of the resistors 272, 274 is connectedto the input of the driver circuit 254.

The idle mode of the power circuit 132 b is substantially the same asthe idle mode described above in connection with the power circuit 132a. During the idle mode of the power circuit 132 b, the comparator 222generates a relatively high voltage on its output. That high voltagecauses the voltage at the output of each of the diodes 264, 266 to behigh, which in turn causes the voltage output by the driver circuits254, 256 to be high, which in turn causes both of the transistors 254,256 to be turned on, so that no significant amount of electric currentis provided to the power supply capacitor 186, as described above.

When the output of the comparator 222 is not high, so that the powercircuit 132 b is not in the idle mode, the transistors 204, 206 areswitched on and off at a high rate that is synchronous with the voltageinduced across the internal coil 152 by the external coil 150. At anypoint in time, exactly one of the transistors 204, 206 is turned on,with the other of the transistors 204, 206 being turned off.

The switching of the transistors 204, 206 during the power supply modecauses current to be supplied to the power supply capacitor 186 throughthe transistors 204, 206. In particular, during one half-cycle, electriccurrent will flow from electrical ground at the conductor 144, downthrough the transistor 206, up through the internal coil 152, and downthrough the diode 192 to the conductor 142 where it is supplied tocharge the power supply capacitor 186. During the next half-cycle,electric current will flow from electrical ground at the conductor 144,up through the transistor 204, down through the internal coil 152, andup through the diode 194 to the conductor 142 where it is supplied tocharge the power supply capacitor 186.

It should be noted that, in the power circuit 132 a, current flowsthrough all four of the diodes 192, 194, 196, 198 during the powersupply mode. However, as described above, in the power circuit 132 b,current flows through only two of the diodes, i.e. diodes 192, 194,during the power supply mode. Instead of flowing through the diodes 196,198 in the power circuit 132 b, current flows through the transistors204, 206. That saves electric power since the transistors 204, 206 havea lower voltage drop associated with them than the diodes 196, 198,which results in less power dissipation in the transistors 204, 206 ascompared with the diodes 196, 198.

The switching control of the transistor 204 during the power supply modeis automatically controlled by the voltage V₂₀₄ at the intersection ofthe resistors 272, 274, and the switching control of the transistor 206during the power supply mode is automatically controlled by the voltageV₂₀₆ at the intersection of the resistors 268, 270. The transistor 204is turned on only when V₂₀₄ is a relatively high voltage, and thetransistor 206 is turned on only when V₂₀₆ is a relatively high voltage.

When the diode 192 is turned on by current flow through it from theinternal coil 152 during one half-cycle, the voltage V₂₀₆ is arelatively high voltage, since it is substantially equal to the outputvoltage across the capacitor 186 minus the voltage drop across the diode192. In that case, the transistor 206 is turned on so that the currentflows through the transistor 206, the internal coil 152, and the diode192 as described above.

When the diode 194 is turned on by current flow through it from theinternal coil 152 during the next half-cycle, the voltage V₂₀₄ is arelatively high voltage, since it is substantially equal to the outputvoltage across the capacitor 186 minus the voltage drop across the diode194. In that case, the transistor 204 is turned on so that the currentflows through the transistor 204, the internal coil 152, and the diode194 as described above.

Modifications of the power circuit 132 b shown in FIG. 10 could be made.For example, the diodes 196, 198 could be omitted from the circuit 132b. Alternatively, the diodes 192, 194, 196 and 198 could be omitted, andfour transistors like the transistors 204, 206 (and diodes 208, 210)could be used in their place.

Power Circuit 132 c

FIG. 11 illustrates the internal coil network 30 shown schematically inFIG. 3 and a power circuit 132 c, which is another possible embodimentof the power circuit 132 schematically shown in FIG. 3. Referring toFIG. 11, the power circuit 132 c is similar to the power circuit 132 ashown in FIG. 6 and described above, except that a voltage modulatingcircuit 280 is included.

The voltage modulating circuit 280 could be provided in the form of aswitching transistor 282 and a resistor 284 connected in series, thecombination of which is connected in parallel with the resistor 228. Itshould be noted that when the transistor 282 is turned on, via a datasignal provided to its input, the resistor 284 is effectively inparallel with the resistor 228. It should be noted that the combinedresistance of the parallel-connected resistors 228, 284 is lower thanthe resistance of the resistor 228 alone. Consequently, that lowercombined resistance lowers the value of V_(SENSE) (with respect toV_(OUT)) provided to the noninverting input of the comparator 222, whichis used to control the voltage limits on the power supply capacitor 186,as described above. The reduction of V_(SENSE) will thus result in ahigher output voltage across the capacitor 186. The data signal providedto the transistor 282 may be generated by a signal generator 290, whichmay be a computer or controller programmed with appropriate software,for example, or another type of signal generator.

FIG. 8 illustrates how the output voltage V_(OUT) across the powersupply capacitor 186 may change in response to the switching of thetransistor 282. Referring to FIG. 8, V_(OUT) is shown to vary between avariable upper limit or envelope 292 and a variable lower limit orenvelope 294. The upper envelope 292 may have a relatively high valueduring each period of time during which the transistor 282 is switchedon, and the upper envelope signal 292 may have a relatively low valueduring each period of time during which the transistor 282 is switchedoff. Similarly, the lower envelope 294 may have a relatively high valueduring each period of time during which the transistor 282 is switchedon, and the lower envelope signal 294 may have a relatively low valueduring each period of time during which the transistor 282 is switchedoff.

It should be noted that the magnitude changes of the upper and lowerenvelopes 292, 294 coincide with the magnitude changes of the datasignal, noted above, used to control the transistor 282. FIG. 9Aillustrates a data signal 296 that, when provided to control thetransistor 282, would result in the output voltage V_(OUT) having theenvelopes 292, 294. The data signal 296 has portions with a relativelyhigh magnitude that may be used to represent logic “1” and portions witha relatively low magnitude that may be used to represent logic “0,” asshown in FIG. 9A. The data signal 296 could be used as a transmit datasignal in order to transmit desired data;which may be represented byvarious combinations of logic “1” and logic “0.”

Alternatively, other methods of data encoding could be used. Forexample, instead of a logic “1” being represented by a relatively largemagnitude and a logic “0” being represented by a relatively smallmagnitude, a data signal could be utilized in which logic “1” isrepresented by a high-frequency portion of the data signal and in whichlogic “0” is represented by a low-frequency portion of the data signal,as shown in FIG. 9B by a data signal 298.

Referring to FIG. 8, it should be noted that the frequency of theenvelopes 292, 294 is lower than the frequency at which the outputvoltage V_(OUT) changes. It should also be understood that the rate atwhich V_(OUT) changes in magnitude, and thus its frequency, depends onthe rate at which the motor 52, or other component (s), draw electriccurrent from the power supply capacitor 186.

Alternative Embodiment of External Assembly 90

FIG. 12 is a block diagram of an external assembly 90 a, which isanother possible embodiment of the external assembly 90 schematicallyshown in FIG. 3. The external assembly 90a is used to recover and decodedata from electric power transmitted between the internal coil 152 andthe external coil 150.

Referring to FIG. 12, the external assembly 90a may include the same DCpower source 102, the DC-to-AC converter 104, the external coil network108 and current sensor 114 described above in connection with FIG. 3.The external assembly 90a includes other components designed to generatea data signal from the magnitude of the current that is induced in theexternal coil 150 by the voltage in the internal coil 152.

Referring to FIG. 13A, an exemplary graph of the voltage V_(OUT) on thepower supply capacitor 186 is shown to have three peaks 302 havingrelatively small magnitudes and three peaks 304 having relatively largemagnitudes. Those peaks of different magnitudes may be produced by thevoltage modulating circuit 280 described above and may representdifferent data values as described above in connection with FIGS. 8 and9A.

FIG. 13B illustrates a bipolar envelope waveform 306 of the relativelyhigh-frequency, bipolar voltage V_(INT) across the internal coil 152that would correspond to the voltage V_(OUT) shown in FIG. 13A. Theenvelope waveform 306 has relatively small positive and negativemagnitudes 308 when the magnitude of V_(OUT) is decreasing andrelatively large positive and negative magnitudes 310 when the magnitudeof V_(OUT) is increasing.

FIG. 13C illustrates a bipolar envelope waveform 312 of the relativelyhigh-frequency, bipolar current I_(EXT) that would be induced in theexternal coil 150 in response to the voltage V_(INT) shown in FIG. 13B.The envelope waveform 312 is similar in the envelope waveform 306 andhas relatively small positive and negative magnitudes 314 when themagnitude of V_(OUT) is decreasing and relatively large positive andnegative magnitudes 316 when the magnitude of V_(OUT) is increasing.

Referring to FIG. 12, the current sensor 114 may be provided to detectthe relatively high-frequency current I_(EXT), such as shown in FIG.13C, passing through the external coil 150. A signal representative ofthe current I_(EXT) may be provided to a rectifier/filter circuit 320via a conductor 322, to a low-pass filter circuit 324 via a conductor326, and to a peak detector 328 via a conductor 330. Referring also toFIG. 13D, the rectifier/filter circuit 320 could be used to generate amagnitude signal I_(MAG) 340 (which is actually a voltage) on theconductor 326, with the I_(MAG) signal having relatively small magnitudeportions 342 when I_(EXT) has relatively small magnitudes and havingrelatively large magnitude portions 344 when I_(EXT) has relativelylarge magnitudes.

Referring to FIGS. 13A-13D, it should be noted that the V_(INT), I_(EXT)and I_(MAG) waveforms have three trapezoidally shaped portions with arelatively small magnitude, which correspond to the peaks 302 of theV_(OUT) waveform, and three trapezoidally shaped portions with arelatively large magnitude, which correspond to the peaks 304 of theV_(OUT) waveform.

Referring also to FIG. 12, the I_(MAG) signal 340 may be provided to acomparator 350 having an inverting input coupled to the conductor 326and a noninverting input coupled to a threshold voltage V_(THRESH). Thecomparator 350 may be used to control a sample and hold circuit 352,which samples and stores the peak values I_(PEAK) of the I_(MAG) signal,via a conductor 354.

The comparator 350 may generate a control signal SAMPLE 360 (FIG. 13E)having relatively small magnitude portions 362 when the value of I_(MAG)is larger than V_(THRESH) and relatively large magnitude portions 364when the value of I_(MAG) is smaller than V_(THRESH).

The sample and hold circuit 352 may be triggered on the rising edge ofthe SAMPLE signal so that the circuit 352 samples and stores voltagesrepresenting the peak values of the I_(MAG) signal. A waveform I_(PEAK)370 representing such peak voltage values is shown in FIG. 13F. TheI_(PEAK) waveform 370 is shown to have three peaks 372 with relativelysmall magnitudes (and which correspond to the peaks 302 of V_(OUT) shownin FIG. 13A) and three peaks 374 with relatively large magnitudes (andwhich correspond to the peaks 304 of V_(OUT) shown in FIG. 13A).

The output of the sample and hold circuit 352 may be provided tobandpass amplifier 380 for further signal processing via a line 382, andthen to the noninverting input of a comparator 384 via a line 386. Athreshold voltage V_(THRESH) may be provided to the inverting input ofthe comparator 384 in order to generate a DATA signal 390 (FIG. 13G)having relatively low magnitudes 392 when the magnitude of the I_(PEAK)signal 370 does not exceed the V_(THRESH) voltage supplied to thecomparator 384 and having relatively high magnitudes 394 when themagnitude of the I_(PEAK) signal 370 exceeds the V_(THRESH) voltagesupplied to the comparator 384. The DATA signal 390 may be provided to acontroller 400 for further processing or other purposes.

Referring to FIG. 20, the controller 400 could comprise various hardwarecomponents, including a random-access memory (RAM) 401, a program memory402, such as a read-only memory (ROM) for storing a computer program, amicroprocessor 403, an input/output (I/O) circuit 404, all of which areinterconnected by an address/data bus 405. Other types of controllerscould be utilized.

Although a particular decoding circuit for recovering data from thepower transmitted from the internal coil 152 to the external coil 150 isdescribed above, other decoding circuits could be utilized.

Frequency Detection

The data transmitted by modulating the voltage across the power supplycapacitor 186 as described above could be frequency modulated in orderto transmit data regarding the operation of the artificial heartassembly 10. For example, in order to communicate a fault condition fromthe internal assembly 100 to the external assembly 90, the voltageacross the power supply capacitor 186 could be modulated so that thedata signal 390 shown in FIG. 13G has a first frequency, such as 50 Hz,and in order to communicate that the internal assembly 100 isfunctioning properly, the voltage across the power supply capacitor 186could be modulated so that the data signal 390 shown in FIG. 13G has asecond frequency, such as 100 Hz. Additional frequencies could be usedto communicate other conditions of the internal assembly 100.

FIGS. 14 and 15 are flowcharts of a pair of computer program routines410, 430 that could be performed by the controller 400 (FIG. 12) todetermine frequency of the data signal 390. The computer programroutines 410, 430 could be stored in memory, such as in the programmemory 402 shown in FIG. 20. The purpose of the analyze period routine410 shown in FIG. 14 is to measure the periods of the data signal 390shown in FIG. 13G and to determine whether portions of the data signal390 correspond to one of a number of predetermined signal frequenciesthat may be used to communicate various messages or conditions of theinternal assembly 100. The analyze period routine 410 may be aninterrupt service routine that is performed once for each detected cycleof the data signal 390, such as upon each rising edge of the data signal390.

Referring to FIG. 14, at block 412, the period T of the most recentlydetected cycle of the data signal 390 is determined. The period may bedetermined, for example, by starting a clock or timer (not shown) upondetection of one rising edge of the data signal 390, and stopping theclock or timer upon detection of the next rising edge of the data signal390.

At block 414, the routine determines whether the measured period Tcorresponds to a frequency that is one of the predetermined signallingfrequencies. If not, the change in the data signal 390 could simply havebeen caused by electrical noise or other interference. At block 414, thetime duration of the period T is compared with a minimum period durationT1 _(MIN) and a maximum period duration T1 _(MAX). For example, if adata signal having a frequency of 100 Hz is being detected, T1 _(MIN)could be set to eight milliseconds and T1 _(MAX) could be set to 12milliseconds since a 100 Hz frequency signal should have cycles withperiods of 10 milliseconds.

If the time duration of the period T is between the upper and lowervalues, then it is assumed that that cycle of the data signal 390 is ofthe signalling frequency corresponding to the period T1, and the routinebranches to block 416 where a count (“T1 COUNT”) of the number ofdetected cycles of that frequency is incremented by one.

Blocks 418 and 420 may be performed to detect another signallingfrequency, such as 50 Hz (for which the corresponding period is 20milliseconds in duration), by determining whether the current cycle ofthe data signal 390 has a period T that is between a minimum period T2_(MAX), such as 16 milliseconds, and a maximum period T2 _(MAX), such as24 milliseconds. Although the routine 410 of FIG. 14 is shown to checkfor the presence of two signalling frequencies, the routine 410 couldtest for any number of signalling frequencies.

The frequency detect routine 430 of FIG. 15 is performed less frequentlythan the routine 410 of FIG. 14, such as once every 10 or 20 times theroutine 410 is performed, or alternatively, on a periodic basis such asonce every second. The purpose of the routine 430 is to determinewhether the data signal 390 corresponds to one of the signallingfrequencies. In that case, it would be expected that all or a highpercentage of the periods T previously measured by the analyze periodroutine 410 would have corresponded to the expected periods for thatsignalling frequency.

For example, assume that the data signal 390 is being transmitted at a100 Hz signalling frequency (in which case T1 _(MIN) might be eightmilliseconds and T2 _(MAX) might be 12 milliseconds), and that thefrequency detect routine 430 is performed once every second. In thatcase, if the signal 390 were a perfect 100 Hz signal, the value of T1COUNT would be 100 since 100 periods T within the expected period rangewould have been detected. However, since the data signal 390 may becorrupted by noise, a lower threshold number may be used. For example,if only 80 periods T within the period limits T1 _(MIN) and T1 _(MAX)are detected (as indicated by the value of T1 COUNT), the signal 390will be recognized as a valid 100 Hz signalling frequency.

The above determination is carried out by the frequency detect routine430 as follows. At block 432, the value of T1 COUNT is compared with apredetermined number THRESH1. If the value of T1 COUNT is larger thanTHRESH1, it is assumed that the data signal 390 is a valid signallingfrequency, and the routine branches to block 434 where a first frequencyflag is set to indicate such assumption. Other actions may also beperformed in that case, such as the display of a message or thegeneration of an audible signal by the external assembly 90. Blocks 436and 438 are performed to test for the presence of a second signallingfrequency. At block 440, the values of T1 COUNT and T2 COUNT are resetto zero.

Energy-Recovery Mode

An alternative embodiment of a DC-to-AC converter 104 a is shown inFIGS. 18A and 18B. The DC-to-AC converter 104 a includes four diodes450, 452, 454, 456, each of which is connected in parallel with one ofthe transistors 170, 172, 174, 176. The diodes 450, 452, 454, 456 may beintegrally formed with the transistors 170, 172, 174, 176 on the samepiece of semiconductive material.

The artificial heart assembly 10 may be operated in a power-supply modein which the DC-to-AC converter 104 a is driven at a relatively highfrequency, such as 200 kHz, and in an idle mode in which the DC-to-ACconverter 104 a is driven at a relatively low frequency, such as about28 kHz. FIGS. 16A and 16B illustrate a pair of drive signals that may beused to drive the DC-to-AC converter 104 a in such a fashion.

When the system switches from the power mode to the idle mode, thecurrents in the coils 150, 152 change from a high level to a low level.Due to the resonant properties of the loosely coupled coil networks 108,130, this change in current takes a decay time that lasts many timeslonger than the period of the resonant frequency of the coil networks.During that decay time, alternating current continues to flow in thecoils 150, 152 at the resonant frequency, which is referred to as“ringing.” That energy is normally dissipated as heat in the coils 150,152 and other circuit components.

The ringing described above will occur when two of the transistors170-176 are on and when two of them are off, as indicated by the DRIVE Aand DRIVE B signals shown in FIGS. 16A and 16B. Referring to FIGS. 16Aand 18A, assume that the DRIVE A signal of FIG. 16A is connected todrive the transistors 170, 176 and that the DRIVE B signal is connectedto drive the transistors 172, 174. When the circuit 104 a transitionsfrom the power mode to the idle mode, the transistors 170, 176 will beturned on for a relatively long period of time, during which they willessentially act as short circuits, and the transistors 172, 174 will beturned off for a relatively long period of time, during which they willessentially act as open circuits.

Consequently, when the circuit 104 a transitions to the idle mode,during one half-cycle of the bidirectional ringing current, current willflow from electrical ground, through the transistor 176, through thecapacitor 148 and the external coil 150, through the transistor 170, tothe DC power source 102 (which is shown in FIG. 2 and represented by +Vin FIGS. 18A and 18B), as indicated by the bidirectional arrow shown inFIG. 18A. During the next half-cycle of the ringing current, currentwill flow through those same components, but in the opposite direction.During the ringing noted above, electrical power will be wasted due todissipation through the components of the circuit 104 a.

In order to conserve electric power, the circuit 104 a may be operatedin an energy-recovery mode before the idle mode begins. During theenergy-recovery mode, instead of turning two of the transistors 170-176on and two of the transistors 170-176 off in accordance with the lowerswitching frequency, all four of the transistors 170-176 aresimultaneously turned off for a period of time.

FIGS. 17A and 17B illustrate exemplary drive signals in the form of aDRIVE C signal and a DRIVE D signal. As shown, both of those drivesignals are low, or logic “0,” during the energy recovery period so thatall four of the transistors 170-176 are turned off, and arenon-conductive, during the energy-recovery period. The energy-recoveryperiod may last, for example, about 20 microseconds or about four fullcycles of the relatively high frequency used to drive the circuit 104 aduring the power-supply mode.

FIG. 18B illustrates the current flows that occur during ringing whenthe circuit 104 a is in the energy-recovery mode. Referring to FIG. 18B,when the circuit 104 a transitions to the energy-recovery mode, duringone half-cycle of the bidirectional ringing current, current will flowfrom electrical ground, upwards through the diode 456, through thecapacitor 148 and the external coil 150, upwards through the diode 450and into the power source 102, as indicated by the arrow 460 shown inFIG. 18B. During the next half-cycle of the ringing current, currentwill flow from electrical ground, upwards through the diode 452, throughthe external coil 150 and the capacitor 148, upwards through the diode454 and into the power source 102, as indicated by the arrow 462 shownin FIG. 18B.

It should be noted that, during both half-cycles of the ringing currentdescribed above in connection with FIG. 18B, current flows fromelectrical ground into the power source 102. Consequently, electricpower is recovered by the power source 102. In contrast, during everyother half-cycle of the ringing current described above in connectionwith FIG. 18A, current flows out of the power source 102.

FIG. 19 illustrates the DC-to-AC converter 104 a and a control circuit116 b, which is an alternative embodiment of the controller 116 shownschematically in FIG. 3, which may be used to drive the converter 104 ain the energy-recovery mode described above.

Referring to FIG. 19, the control circuit 116 b includes therectifier/filter circuit 240, the comparator 242, the selector switch244, the frequency generator 246 and the frequency divider 248, all ofwhich operate as described above in connection with FIG. 5.

The control circuit 116 b includes additional circuitry that is used toforce the drive signals to a value, such as logic “0,” that causes thetransistors 170-176 to be turned off during the energy-recovery period.That additional circuitry may be provided in the form of a delay element470, which may be a timer or one-shot, that is coupled to the output ofthe comparator 242 via a conductor 472. The output of the delay element470 may be connected to one input of each of a pair of AND gates 474,476. The drive signals output from the selector switch 244 are providedto a second input of each of the AND gates 474, 476. As described above,the comparator 242 can detect when the artificial heart assembly 10transitions from the power-supply mode to the idle mode (in which casethe output of the comparator 242 will change from logic “1” to logic“0”).

Upon detecting a change in the output of the comparator 242, the delayelement 470 will force the outputs of the AND gates 474, 476 to logic“0,” causing all four transistors 170-176 to be turned off, bytransmitting a logic “0” signal to one of the inputs of each of the ANDgates 474, 476 for the time period corresponding to the energy-recoverymode.

Additional details may be disclosed in the following patentapplications, for which William Weiss is the named inventor, each ofwhich is incorporated by reference herein: U.S. Ser. No. 09/557,813filed herewith and entitled “Artificial Heart Power Supply System”; U.S.Ser. No. 09/557,814 filed herewith and entitled “Artificial Heart WithSynchronous Rectification”; U.S. Ser. No. 09/557,809 filed herewith andentitled “Artificial Heart Data Communication System”; and U.S. Ser. No.09/557,810 filed herewith and entitled “Artificial Heart With MetalDetection.”

Metal Detection

The operation of the artificial heart assembly 10 may be adverselyaffected if one or both of the external and internal coils 150, 152comes relatively close to either a conductive material, such as metal,or a magnetically permeable material, such as ferrite. If such amaterial comes in close proximity with one of the coils 150, 152, theinductive coupling between the coils 150, 152 will be altered, thuschanging the power transmission characteristics between the coils 150,152 in an unintended and possibly adverse manner. In such case, deliveryof electric power to the internal portions of the artificial heartassembly 10 may be disrupted, and the internal or external electricalcomponents of the artificial heart assembly 10 may be damaged.

Conductive materials and magnetically permeable materials whichinterfere with the inductive coupling of the coils 150, 152 and theirpower transmission characteristics are collectively referred to hereinas “interfering materials.” The close proximity of an interferingmaterial to one of the coils 150, 152 may change one or both of theinductances L_(INT) and L_(EXT) described above, resulting in de-tuningof the resonant circuit formed by the coils 150, 152. The closeproximity of an interfering material may also alter the magnetic fluxlinkage between the coils 150, 152.

The artificial heart assembly 10 may be designed to detect when aninterfering material comes in relatively close proximity with one of thecoils 150, 152 and may be designed to cause a remedial action to beundertaken in response thereto. For example, upon detection that aninterfering material is in close proximity to one of the coils 150, 152,the artificial heart assembly 10 could generate an alarm, such as avisual or audible warning, and/or could prevent power from beingprovided to the external coil 150.

The detection of an interfering material in proximity with one of thecoils 150, 152 could be based on the detection of a phase shift betweenthe voltage supplied by the external coil 150 and the current thatpasses through the external coil 150. Alternatively, the proximity of aninterfering material could be based upon the detection or determinationof other characteristics of one or both of the coils 150, 152, such asbased on the magnitude of the current flowing through the external coil150.

FIG. 22 is a block diagram of one possible embodiment of a detectioncircuit 500 that detects the proximity of an interfering material andcauses one or more remedial actions to be taken in response thereto. Thedetection circuit 500 shown in FIG. 22 is similar to the circuit 116 bshown in FIG. 19 to the extent that the detection circuit 500 includesthe components 182, 240, 242, 244, 246, 248, 474 and 476, the operationof which is described above. only the new components of the detectioncircuit 500 are described below.

Referring to FIG. 22, the detection circuit 500 may be provided with asquare-wave generating circuit, such as a zero-crossing detector 502,that is coupled to receive the signal on the line 118 generated by thecurrent sensor 114 (FIG. 3), which signal has the same frequency and mayhave substantially the same phase as the current passing through theexternal coil 150. From the signal on the line 118, which may begenerally sinusoidally shaped, the square-wave generating circuit 502may generate a square wave having the same frequency and substantiallythe same phase as the signal on the line 118. The output of the circuit502, which is representative of the frequency and phase of the currentpassing through the external coil 150, is provided to one input of aphase detector 504 via a line 506.

The phase of the voltage that is supplied to the external coil 150(which may be the voltage provided across the external coil network 108)is generally the same as the phase of the logic-level signal(s) used todrive the DC-to-AC converter 104 (FIG. 3). Consequently, the output ofthe frequency generator 246 is representative of the phase of thevoltage supplied to the external coil 150 and may be coupled to a secondinput of the phase detector 504 via a line 508.

The phase detector 504 may detect or determine the magnitude of thephase shift between the two signals provided via the lines 506, 508,such as by determining the time delay between the rising edge of thesignal on the line 506 and the rising edge of the signal on the line508. The phase detector 504 may provide a signal representative of themagnitude of the phase shift to a controller 510 via a line 512, and thephase detector 504 may also provide a signal representative of the phasesign to the controller via the line 512 (which may be a multi-conductorline) to indicate whether the voltage provided to the external coil 150is leading or lagging the current (as measured) passing through theexternal coil 150.

In response to the signal(s) provided via the line 512, the controller510 may take one or more remedial actions. The controller 510 may causea visual, audible or other type of alarm or warning to be generated byactivating an alarm generator 514 via a line 516. Depending on themagnitude phase shift, the controller 510 may also prevent power frombeing supplied to the external coil 150. That may be accomplished bytransmitting a disable signal (e.g. logic “0” signal) to the AND gates474, 476 via a line 518 to cause the transistors 170, 172, 174, 176(FIG. 4) to become nonconductive.

The detection circuit 500 shown in FIG. 22 does not include the delaycircuit 470 shown in FIG. 19, which may be used for idle-mode operationas described above. If it were desired to use both the idle-modeoperation and the phase detection capability, the output of thecomparator 242 could be connected to be received by the controller 510,and the controller 510 could be programmed or otherwise designed tosimulate the operation of the delay circuit 470 by disabling theDC-to-AC converter 104 (via the line 518) a predetermined delay periodafter receiving an idle signal from the output of the comparator 242.

If a phase detector is used to detect the proximity of an interferingmaterial, the phase detector 504 shown in FIG. 23 could be utilized.Referring to FIG. 23, a signal representative of the phase of thevoltage that is supplied to the external coil 150 is supplied to thephase detector 504 via the line 508, and a signal representative of orbased on the phase of the current that passes through the external coil150 is supplied to the phase detector 504 via the line 506.

The phase detector 504 may be provided with a first circuit, which maybe in the form of a D flip-flop 530, that determines the sign of thephase difference between the voltage and current, i.e. whether thevoltage leads or lags the current. A D flip-flop may operate by passingthe value of its input (designated “D”) to its output (designated “Q”)upon each rising edge of a signal provided to its clock input (shown bya triangle), and by forcing its output to zero if a logic “0” signal isprovided to its clear input (designated “CLRN”). The preset input(designated “PRN”) of the flip-flop 530 is not utilized since it isactivated by a logic “0” signal and since that input is tied to a highor logic “1” voltage (in the form of “VCC”).

For a D flip-flop as described above, if the voltage leads the current,as shown in FIGS. 24A and 24B, the flip-flop 530 will generate a logic“0” output (as shown in FIG. 24C) since the value of the current signalis low or logic “0” at each rising edge of the voltage signal. If thevoltage lags the current, the flip-flop 530 will generate a logic “1”output since the value of the current signal is high or logic “1” ateach rising edge of the voltage signal.

The detection circuit 504 may be provided with a D flip-flop 532 thatgenerates a pulse having a duration corresponding to the phasedifference or shift between the voltage and current when the voltageleads the current. Since the input of the flip-flop 532 is tied to ahigh or logic “1” voltage, the flip-flop 532 generates a high outputupon the rising edge of the voltage signal on the line 508. That outputfalls to zero upon the rising edge of the current signal provided on theline 506 due to the current signal being provided to the clear input ofthe flip-flop 532. For the case where the voltage leads the current asshown in FIGS. 24A and 24B, FIG. 24D illustrates the shape of the outputof the flip-flop 532, which output is designated PHASE_(V). It can beseen that the duration or width of the PHASE_(V) pulses corresponds tothe phase difference between the voltage and current signals shown inFIGS. 24A and 24B.

The phase detection circuit 504 may be provided with a D flip-flop 534that operates in the same manner as the flip-flop 532 described above todetermine the magnitude of the phase difference between the voltage andcurrent in the case where the current leads the voltage. For the casewhere the current does not lead the voltage as shown in FIGS. 24A and24B, FIG. 24E illustrates the shape of the output of the flip-flop 534,which output is designated PHASE_(I), as a constant, relatively lowvoltage since the current does not lead the voltage. If the current didlead the voltage, the PHASE_(I) signal would have a duration or widthcorresponding to the phase shift between the leading current signal andthe lagging voltage signal.

The detection circuit 504 may be provided with a data selector circuit540 in order to select either the output of the flip-flop 532 or theoutput of the flip-flop 534, depending on whether the voltage leads orlags the current.

The data selector circuit 540 may be composed of an inverter 542, a pairof AND gates 544, 546, and an OR gate 548. The output of the flip-flop530, which is indicative of whether the voltage leads or lags thecurrent, is provided to the AND gate 546, and the complemented output ofthe flip-flop 530 is provided to the AND gate 544. Thus, at any time,only one of the AND gates 544, 546 will be selected (by providing alogic “1” thereto) in order to provide its output to the OR gate 548.Where the voltage leads the current as shown in FIGS. 24A and 24B, thelogic “0” output of the flip-flop 530 enables the AND gate 544 to causethe output (V_(MAG)) of the flip-flop 532 to be passed through the ANDgate 544 to the OR gate 548.

The output of the OR gate 548, which represents the magnitude of thephase shift between the voltage and current, may be provided to atri-state element or buffer 550 before being provided to a chargestorage circuit, such as a low-pass filter circuit 552 having a chargingcapacitor (not shown). The tri-state element 550 may be used in caseswhere the phase detector 504 is not used all of the time.

For example, if the idle-mode feature described above is utilized, thephase detector 504 may be disabled during idle mode. In that case, anidle-mode signal indicating that the artificial heart assembly 10 isoperating in the idle mode may be provided to the tri-state element 550to cause it to enter a high-impedance state so that the value of thecurrent phase shift magnitude signal of the charge storage circuit 552is maintained regardless of the output of the OR gate 548. The idle-modesignal provided to the tri-state element 550 could be generated from theoutput of the comparator 242 (FIG. 22).

It should be understood that phase detection circuits are conventionaland that there are numerous types of such circuits. Thus, the phasedetection circuit shown in FIG. 23 is exemplary only and numerous othertypes of phase detection circuits could be utilized. Also, as notedabove, detection circuits other than phase detection circuits could beutilized.

During normal operation of the artificial heart assembly 10 without aninterfering material in close proximity with either of the coils 150,152, the voltage supplied to the external coil 150 and the current thatpasses through the external coil 152 may have the same phase. When aninterfering material comes in close proximity to one of the coils 150,the material induces a phase shift between the current and voltage. Themagnitude and direction of the phase shift may depend on how close theinterfering material is and whether the interfering material is closerto the external coil 150 or to the internal coil 152.

FIG. 21 illustrates a range of current-voltage phase relationships onwhich the operation of the artificial heart apparatus 10 may be based.In FIG. 21, a positive phase relationship is one in which the voltageleads the current, and a negative phase relationship is one where thevoltage lags the current. The phase relationships shown in FIG. 21 maynot represent the actual phase relationships of voltage that is suppliedto the external coil 150 and the current that passes through theexternal coil 150 due to phase delays caused by measurement. Forexample, the signal generated by the current sensor 114 (FIG. 1) may bedelayed somewhat in phase with respect to the actual current passingthrough the external coil 150. Also, the zero-crossing detector 502 maygenerate a signal delay. However, even with delays induced bymeasurement, it should be understood that the close proximity of aninterfering material will cause substantially the same phase shift inthe measured signals as it does in the actual current and voltage.

Still referring to FIG. 21, during operation of the artificial heartassembly 10 without an interfering material in close proximity with oneof the coils 150, 152, there may be a range of normal phaserelationships in which there is a given range of measured phasedifferences between voltage and current. Upon an interfering materialcoming into proximity with one of the coils 150, 152, the magnitude ofthe phase shift may decrease to a warning level (as indicated by adotted line), upon which an audible or visual warning may be generated.Upon the interfering material coming into closer proximity with one ofthe coils 150, 152, the magnitude of the phase shift may furtherdecrease to a fault level, upon which the supply of power to theexternal coil 150 may be suspended or interrupted.

FIG. 25 is a flowchart of a metal detect routine 560 illustrating anumber of actions that could be periodically performed (e.g. once everysecond) by the controller 510 shown in FIG. 22. The controller 510 couldhave the components shown in FIG. 20, in which case a computer programthat performs the actions shown in FIG. 25 could be stored in theprogram memory 402 (FIG. 20) and performed by the microprocessor 403.

Referring to FIG. 25, at block 562, the magnitude of the phasedifference is read by the controller 510, which phase difference may bethat generated on the line 512 b shown in FIG. 23. If the magnitude ofthe phase difference is less than a warning threshold limit asdetermined at block 564, the program may branch to block 566 where awarning flag may be set to cause a first type of remedial action to beperformed, such as the generation of an audible or visible alarm.

If the magnitude of the phase difference read at block 562 is less thana fault threshold limit as determined at block 568, the program maybranch to block 570 where a fault flag may be set to cause a second typeof remedial action to be performed, such as the interruption in thesupply of power to the external coil 150 (which may be accomplished viaa logic “0” signal being generated by the controller 510 on the line 518in FIG. 22).

At block 572, the sign of the phase difference may be read from the line512 a shown in FIG. 23. At block 574, if the sign of the phasedifference is logic “1,” meaning that the current is leading thevoltage, a fault flag may be set at block 576.

It should be understood that not all actions shown in FIG. 25 arenecessary, and various actions could be eliminated or modified. Forexample, blocks 572-576 could be eliminated and blocks 562-570 could bemodified to act upon the magnitude of the current that passes throughthe external coil 150 instead of the phase difference between thevoltage and current as described above.

Numerous additional modifications and alternative embodiments of theinvention will be apparent to those skilled in the art in view of theforegoing description. This description is to be construed asillustrative only, and is for the purpose of teaching those skilled inthe art the best mode of carrying out the invention. The details of thestructure and method may be varied substantially without departing fromthe spirit of the invention, and the exclusive use of all modificationswhich come within the scope of the appended claims is reserved.

What is claimed is:
 1. An artificial heart assembly, comprising: a bloodinlet conduit; a blood outlet conduit; a pump that is adapted to pumpblood from said blood inlet conduit to said blood outlet conduit; aninternal coil adapted to be implanted beneath the skin of a subject; anexternal coil adapted to be disposed adjacent said internal coil andseparated from said internal coil by the skin of a subject, saidexternal coil being coupled to transmit electric power to said internalcoil through the skin of a subject; and a DC-to-AC converter coupled tosaid external coil and to a source of DC power, said DC-to-AC converterselectively converting DC power from said DC power source into either afirst frequency or a second frequency, said first frequency having aplurality of cycles each of a first duration and said second frequencyhaving a plurality of cycles each of a second duration longer than saidfirst duration, said DC-to-AC converter comprising: a first transistorcoupled in parallel with a first diode; a second transistor coupled inparallel with a second diode; a third transistor coupled in parallelwith a third diode; a fourth transistor coupled in parallel with afourth diode; and a drive circuit operatively coupled to saidtransistors, said drive circuit causing all four of said transistors tobe switched to a nonconductive state so that said four transistors arenonconductive for a time period.
 2. An artificial heart assembly asdefined in claim 1 wherein said drive circuit causes all four of saidtransistors to be switched to a nonconductive state for a time period atleast as long as said first duration.
 3. An artificial heart assembly asdefined in claim 1 wherein said drive circuit causes all four of saidtransistors to be switched to a nonconductive state for a time period atleast twice as long as said first duration.
 4. An artificial heartassembly as defined in claim 1 wherein said DC-to-AC converter isoperable in a power-supply mode and an idle mode, wherein said DC-to-ACconverter converts DC power from said DC power source into said firstfrequency during said power-supply mode, and wherein said DC-to-ACconverter converts DC power from said DC power source into said secondfrequency during said idle mode.
 5. An artificial heart assembly asdefined in claim 1 wherein said DC-to-AC converter is operable in apower-supply mode and an idle mode, wherein said DC-to-AC converterconverts DC power from said DC power source into said first frequencyduring said power-supply mode, wherein said DC-to-AC converter convertsDC power from said DC power source into said second frequency duringsaid idle mode, and wherein said first frequency is a multiple of saidsecond frequency.
 6. An artificial heart assembly as defined in claim 1wherein said first transistor is connected to said second transistor ata first junction, wherein said second transistor is connected to saidthird transistor at a second junction, wherein said third transistor isconnected to said fourth transistor at a third junction, and whereinsaid fourth transistor is connected to said first transistor at a fourthjunction.
 7. An artificial heart assembly as defined in claim 6 whereinsaid fourth junction is connected to said DC power source, wherein saidsecond junction is connected to a ground potential, and wherein saidexternal coil is connected between said first and third junctions.
 8. Anartificial heart assembly as defined in claim 1 additionally comprisinga membrane defining a blood chamber fluidly coupled to said blood inletconduit and said blood outlet conduit, wherein said pump comprises apusher member which makes contact with said membrane to force blood fromsaid blood inlet conduit to said blood outlet conduit.
 9. An artificialheart assembly as defined in claim 1 additionally comprising: a firstmembrane defining a blood chamber fluidly coupled to said blood inletconduit and said blood outlet conduit, wherein said pump comprises apusher member which makes contact with said first membrane to forceblood from said blood inlet conduit to said blood outlet conduit; asecond membrane defining a second blood chamber fluidly coupled to asecond blood inlet conduit and a second blood outlet conduit; and asecond pusher member which makes contact with said second membrane toforce blood from said second blood inlet conduit to said second bloodoutlet conduit.
 10. An artificial heart assembly, comprising: a bloodinlet conduit; a blood outlet conduit; a pump that is adapted to pumpblood from said blood inlet conduit to said blood outlet conduit; aninternal coil adapted to be implanted beneath the skin of a subject; anexternal coil adapted to be disposed adjacent said internal coil andseparated from said internal coil by the skin of a subject, saidexternal coil being coupled to transmit electric power to said internalcoil through the skin of a subject; and a DC-to-AC converter coupled tosaid external coil and to a source of DC power, said DC-to-AC converterselectively converting DC power from said DC power source into either afirst frequency or a second frequency, said first frequency having aplurality of cycles each of a first duration and said second frequencyhaving a plurality of cycles each of a second duration longer than saidfirst duration, said DC-to-AC converter comprising: a first switchingcomponent coupled in parallel with a first passive component; a secondswitching component coupled in parallel with a second passive component;a third switching component coupled in parallel with a third passivecomponent; a fourth switching component coupled in parallel with afourth passive component; and a drive circuit operatively coupled tosaid switching components, said drive circuit causing all four of saidswitching components to be switched to a nonconductive state so thatsaid four switching components are nonconductive for a time period andso that electric current flows through a plurality of said passivecomponents during said time period.
 11. An artificial heart assembly asdefined in claim 10 wherein said drive circuit causes all four of saidswitching components to be switched to a nonconductive state for a timeperiod at least as long as said first duration.
 12. An artificial heartassembly as defined in claim 10 wherein said drive circuit causes allfour of said switching components to be switched to a nonconductivestate for a time period at least twice as long as said first duration.13. An artificial heart assembly as defined in claim 10 wherein saidfirst switching component is connected to said second switchingcomponent at a first junction, wherein said second switching componentis connected to said third switching component at a second junction,wherein said third switching component is connected to said fourthswitching component at a third junction, and wherein said fourthswitching component is connected to said first switching component at afourth junction.
 14. An artificial heart assembly as defined in claim 13wherein said fourth junction is connected to said DC power source,wherein said second junction is connected to a ground potential, andwherein said external coil is connected between said first and thirdjunctions.
 15. Apparatus for use in an artificial heart assembly havinga blood inlet conduit, a blood outlet conduit, and a pump that isadapted to pump blood from the blood inlet conduit to the blood outletconduit, said apparatus comprising: an internal coil adapted to beimplanted beneath the skin of a subject; an external coil adapted to bedisposed adjacent said internal coil and separated from said internalcoil by the skin of a subject, said external coil being coupled totransmit electric power to said internal coil through the skin of asubject; and a DC-to-AC converter coupled to said external coil and to asource of DC power, said DC-to-AC converter selectively converting DCpower from said DC power source into either a first frequency or asecond frequency, said first frequency having a plurality of cycles eachof a first duration and said second frequency having a plurality ofcycles each of a second duration longer than said first duration, saidDC-to-AC converter comprising: a first switching component coupled inparallel with a first passive component; a second switching componentcoupled in parallel with a second passive component; a third switchingcomponent coupled in parallel with a third passive component; a fourthswitching component coupled in parallel with a fourth passive component;and a drive circuit operatively coupled to said switching components,said drive circuit causing all four of said switching components to beswitched to a nonconductive state so that said four switching componentsare nonconductive for a time period and so that electric current flowsthrough a plurality of said passive components during said time period.16. An apparatus as defined in claim 15 wherein said drive circuitcauses all four of said switching components to be switched to anonconductive state for a time period at least as long as said firstduration.
 17. An apparatus as defined in claim 15 wherein said drivecircuit causes all four of said switching components to be switched to anonconductive state for a time period at least twice as long as saidfirst duration.
 18. An apparatus as defined in claim 15 wherein saidfirst switching component is connected to said second switchingcomponent at a first junction, wherein said second switching componentis connected to said third switching component at a second junction,wherein said third switching component is connected to said fourthswitching component at a third junction, and wherein said fourthswitching component is connected to said first switching component at afourth junction.
 19. An apparatus as defined in claim 18 wherein saidfourth junction is connected to said DC power source, wherein saidsecond junction is connected to a ground potential, and wherein saidexternal coil is connected between said first and third junctions.